Variable buoyancy systems are commonly employed in salvaging objects from the ocean or positioning and recovering oceanographic instrumentation. These buoyancy systems may take several different forms, such as lift bags or ballast tanks. Historically, high pressure air tanks have been utilized for deballasting such buoyancy systems. More recently, various materials have been reacted to generate a gas for deballasting the systems. Hydrazine is commonly reacted to generate a gas, and has been found highly satisfactory for raising objects from the ocean bottom. However, hydrazine is not cost effective and is very hazardous for personnel to handle. Gas generated by reacting metallic hydrides is safer and considerably more cost effective.
Previous metallic hydride gas generating systems have used nonreactive water insoluble hydrocarbons such as hexane, kerosene, mineral oil, and benzene to form extrudable slurries or paste when blended with powdered metallic hydride. Additionally, nonreactive water soluble organic liquids such as tetrahydrofuran, dioxane, and glycol ethers have been incorporated in the slurries to control solubility and, thus, the reaction rates of the metallic hydride with water. Because of the large amount of nonreactive materials required, these slurries have been heavy and bulky. In addition, they are difficult to store and require special handling and pumping equipment.
A recent metallic hydride gas generator is described in U.S. Pat. No. 4,055,632 to Robert T. Hoffman. In this gas generator, metallic hydride pellets are selectively released from a nonreactive liquid to a reactive liquid for the generation of gas. This generator is highly satisfactory for raising small objects, however, a more practical system is required for raising large objects from the ocean bottom. Also, the gas generator described in the patent will not terminate the generation of gas quickly since the pellets must be completely expended once they are disseminated into the reactive liquid.